In the original design, the four lights in the clock - one for each quadrant
- were individually controllable. This design would have allowed for some neat
effects. For example a dark clock except when a clock mode was active. Or, a
rotating light effect in timed modes. Anyhow, the designers ran out of light
circuits so they shoved it onto the GI which opened up all of those clock heat
problems. They do flash the clock in timed modes.

I am scheming about adding some more LEDs to the clock. Red, green, blue and
white in each quadrant. I should be able to add some neat effects - colored
strobes in the last 15 seconds of timed modes, for example. I can deduce what
effect to deliver by the motion of the clock.

However, to do this I have to redesign BOTH clock boards. Well, I could leave
the hours board alone, but the original Williams design is a bit iffy and it
would be nice to get away from the special optos.

Clock Rules

Normal Gameplay: 12 noon

Most timed modes: wind from 12 o'clock to 12 o'clock.

Stacked timed mode: rewind back to 12 o'clock and then run forwards to 12
o'clock. Underlaid mode continues to run. (question: who takes priority?).

Clock chaos: wind back to 6. ind back to 12. reverse direction on a hit. Stop
when the hands hit 12.

Ball drain: hands to 12

Attract mode: show the current time

Design Process

So the first thing is getting the mechanical design sorted out, and
duplicating the basic electronics. Then, we'll design the next phase. There are
some peculiarities in the original design.

First, we all know about the GI lamps, four #86 bulbs that cook up the inside
of the clock. This heating damages the plastics and makes the clock electronics
compartment into a hostile environment. One consequence of this is degradation
of the optocouplers, which combines with the switch circuit problem to cause
premature failure of the clock.

Less obvious is that the power design for the optocoupler LEDs is not
efficient. The LEDs only require 1.2V to do their work, but the supply
delivers 12V. Therefore, there is a 470 ohm resistor in the LED circuit to drop
the 10.8V that we need to get down to 1.2V. This corresponds to a drive current
of 23mA - a little above spec. However, the resistor is dropping 10.8V at 23mA,
which is 250mW. There are eight of these in the clock, that is another 2W of
heat - and it explains why the resistors are often burned up. They get really
hot. Without the GI heat they could be OK, but this is an iffy design.
A better approach is to wire the optocouplers in series, and have a single
resistor dropping the 7.2V that we need. That's 360 ohms. I could run all 8 in
series, but that would make the new and old boards incompatible with each other.

The third problem is the sense circuit, which makes the whole heat
problem worse. It is why we need special sensitive optos. But this is the hand
that we are dealt.

Here's the hours board. This is mostly done; it follows the original
schematic. For some reason, the WIlliams optos use a different pinout to the
ones that I have found. It is a simple change - the device is rotated 180
degrees - but this could certainly mess you up! The good news is that Williams
explicitly labeled the anode, cathode, collector and emitter pins. Note that J1
has one pin too many. This is on the todo list.

There's a lot of open space on this board. I could put quite a lot of stuff
on here, except I don't want to lose backwards compatibility. Make the whole
clock light up, maybe? Perhaps there is a use for that extra pin!

Here's the first draft of the minutes board. This is mostly as Williams
designed it, but it does not yet have lights. Opto 1 is placed backwards; this
needs to be fixed.

Here's the latest version. It has lamps and drivers. This version also uses a
CMOS latch to get away from the opto level issues, and allow me to read the
optos from the microprocessor. The design is going to need a 5V buck regulator,
which will have to go on the hours board: I am running out of PADS resources!
The microprocessor is not connected, no decoupling, and power and ground missing
in action.

You can see the 16 quadrant LEDs in the center are of the board, with their
Maxim LED drivers. The microcontroller is largely disconnected, and is currently
in the top left. The latch and pullups are in the bottom left hand corner.
I can add exactly one more part: probably the clock oscillator for the PIC.
Decoupling caps will have to be opportunistic.